Method for manufacturing a metal organic deposition precursor solution using super-conduction oxide and film superconductor

ABSTRACT

There is provided a method of fabricating a precursor solution for a metal organic deposition method using a superconducting oxide as a starting material, the method including dispersing a superconducting material powder in a TFA acid aqueous solution and heating them to dissolve the powder in the TFA solution; increasing a temperature of a hot substrate if the powder is completely dissolved, and the solution is clear, and continuously heating until the solution is vaporized and is in a viscous jelly state; stopping the heating if the solution loses its flowing property completely, and cooling the solution; and dissolving the compound in the jelly state, hardened at a room temperature, into an organic solvent, to provide metal organic deposition solution for coating. There is also provided a method of fabricating a thin film-typed superconductor using a metal organic deposition method, the method including dispersing a superconducting material powder in a TFA acid aqueous solution and heating them to dissolve the powder in the TFA solution; increasing a temperature of a hot substrate if the powder is completely dissolved, and the solution is clear, and continuously heating until the solution is vaporized and is in a viscous jelly state; stopping the heating if the solution loses its flowing property completely, and cooling the solution; dissolving the compound in the jelly state, hardened at a room temperature, into an organic solvent, to provide a superconducting material powder-TFA precursor solution; after forming a textured oxide buffer layer on a textured metal substrate, or forming a textured oxide template on a metal substrate and forming an oxide buffer layer thereon, dropping the superconducting material powder-TFA precursor solution on the single crystal metal substrate so as to deposit a thin film; and drying it to form the thin film; and applying a calcination heat treatment on the thin film to provide the thin film with a superconducting property. In the method of fabricating a thin film superconducting conductor using REBa 2 Cu 3 O 7-x  (RE=rare earth elements such as Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, etc. or mixture thereof), a precursor solution is fabricated by dissolving REBa 2 Cu 3 O 7-x  (RE=rare earth elements such as Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, etc. or mixture thereof) group of oxide into TFA acid aqueous solution, and using the precursor solution, the superconducting conductor can be provided more easily with a lower price than a conventional precursor solution.

TECHNICAL FIELD

The present invention relates to a method of fabricating a precursor solution using superconducting oxide powder as starting materials, a method of coating a substrate (ceramic, nickel metal, nickel alloy, stainless steel, etc.) with an epitaxial thin film using the precursor solution, and a high-temperature superconductor fabricated by the methods.

BACKGROUND ART

In order to deposit a superconducting thin film containing REBa₂Cu₃O_(7-X) (RE=rare earth elements such as Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, etc. or mixture of the elements) on a metal-oxide template, which is made by depositing a textured oxide coating material on a {100}<100>textured nickel or, a nickel base alloy, or a metal substrate made by epitaxially depositing a nickel on nickel base alloy, or a metal substrate, which is formed by depositing a textured ceramic layer on an alloy such as stainless steel or hastalloy, using a metal organic deposition (MOD) method, it is necessary to fabricate an organic metal precursor solution containing cation ions of oxide superconductors such that an epitaxial thin film is effectively formed during heat treatments for high quality superconducting films with a critical current density over 10⁵ A/cm²

Further, after depositing the organic metal precursor solution on the substrate, it is necessary to effectively control an oxygen partial pressure, a water vapor pressure (P), heat treatment temperature, a heat treatment time, a gas flow, or the like.

However, among metal organic solvents used to fabricate a high-temperature superconducting thin film by a method using such a chemical solution up to now, the one showing the most excellent characteristics is trifluoro-acetatic acid (TFA) solution.

In the typical method of fabricating the precursor solution, which has been used up to now, the precursor solution is made by respectively dissolving yttrium (Y)-acetate, barium (Ba)-acetate, copper (Cu)-acetate into the TFA solution in accordance with cation ratios of a final superconducting product (for example, Y:Ba:Cu=1:2:3), and then, through a vaporizing distillation process and a remelting-polymerization process (refluxing), the precursor solution, in which a cation ratios of Y, Ba, Cu is 1:2:3, is fabricated and deposited on the substrate.

This method is carried out by dissolving acetate materials of Y, Ba, Cu into the TFA solution to form a cationic polymer having 123 composition ratios through a polymerization process, and by gelating to achieve a TFA polymer of Y, Ba, Cu in a jelly state, and by diluting the polymer with methanol, so as to provide a material to be used as a deposition solution.

DISCLOSURE OF INVENTION Technical Problem

In the processes, it is necessary to exactly adjust the respective ratios and the respective purities of Y, Ba, Cu acetate. The cost of the acetate used in this technology is so high, and if a high purity metal acetate is not used, it has a disadvantage that the process and the product are so vulnerable to impurities. Furthermore, it is necessary to precisely control fabrication conditions of the precursor solution in order to fabricate a good polymer. Further, in order to use a rare earth metal other than yttrium, it is necessary to prepare acetate containing other rare earth metal elements, and furthermore, it is difficult to add other elements alloys.

Technical Solution

Therefore, an object of the present invention is to solve the problems involved in the prior art, and to provide a method of fabricating a precursor solution in which cation ratios of a rare earth element or a solid solution thereof rare earth metals (yttrium (Y), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium(Yb), lutetium (Lu) or the like), barium, and copper is preferably 1:2:3.

Another object of the present invention is to provide a method of fabricating a superconducting conductor by epitaxially depositing at least one ceramic buffer layer (one of CeO₂, MgO, YSZ, SrTiO₃, LaAlO₃, RuSrO, Gd₂O₃,Y₂O₃, or their mixture) on a {100}<100> textured metal substrate, and using an MOD method, eptaxially depositing

REBa₂Cu₃O_(7-x) (RE=rare earth elements such as Y, La, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, etc. or mixture thereof) group of a superconducting thin film.

DESCRIPTION OF DRAWINGS

The above objects, other features and advantages of the present invention will become more apparent by describing the preferred embodiment thereof with reference to the accompanying drawings, in which:

FIG. 1 is a view to illustrate processing sequences of a superconducting thin film formation process.

FIG. 2 is a graph to illustrate a process of a calcination heat treatment of a superconducting material powder-TFA solution.

FIG. 3 is a graph to illustrate a process of a conversion heat treatment of a superconducting thin film.

FIG. 4 is a graph to illustrate an X-ray diffraction analysis result of the fabricated superconducting thin film.

FIGS. 5, 6, 7, 8 are views to illustrate micro structures of the fabricated superconducting thin film.

FIG. 9 is a graph to illustrate measurement results of a critical transition temperature of the fabricated superconducting thin film.

FIG. 10 is a graph to illustrate measurement results of a critical current density of the fabricated superconducting thin film.

BEST MODE

The present invention may include the operations of dispersing a superconducting material powder in a TFA acid aqueous solution and heating them to dissolve the powder in the TFA acid aqueous solution; agitating the solution at an elevated temperature until the powder is completely dissolved, and the solution is clear, and maintains the solution at an elevated temperature until the solution is vaporized and is in a viscous jelly state; stopping the heating if the solution loses its flowing property completely, and cooling the solution; and melting the compound in the jelly state, hardened at a room temperature, into an organic solvent preferably methanol, to provide a Yttrium-TFA/Barium-TFA/Copper-TFA solution for coating. Alternately, vaporaization of the dissolved solution is vacuum dried.

Preferably, a total cation concentration of Yttrium-TFA/Barium-TFA/Copper-TFA solution for coating may be in the range of 0.1˜6 mol.

Preferably, the superconducting material powder may be REBa₂Cu₃O_(7-x) (RE=rare earth elements such as Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, etc. or their combination thereof) with a cation ratio of RE:Ba:Cu=1:2:3. But the cation ratio of RE:Ba is varied depending on the selected rare earth metals as RE:Ba=1−x:2(1+x)(−0.2<x<0.2).

Further, the superconducting material powder may preferably use a powder of 123 compound prepared from a mixture of rare earth elements (Ya, Ybb, Smc, Lad, Nde, Hof, Gdg . . . )1Ba2Cu3O7−x (a+b+c+d+e+f+g+ . . . =0<x<0.5).

Preferably, the organic solvent may be one selected from the group consisting of methyl alcohol, ethyl alcohol, methoxy ethanol (methylol glycol monomethyl ether).

In another aspect of the present invention, there is provided a method of fabricating a thin film-typed superconductor using a metal organic deposition method, and the method may include the processing steps dispersing a superconducting material powder in a TFA acid aqueous solution and heating them to dissolve the powder in the TFA solution; keeping the TFA acid aqueous solution until the powder is completely dissolved, and the solution is clear, and maintaining the solution at elevated temperature until the solution is vaporized and is in a viscous jelly state; stopping the heating if the solution loses its fluidity completely, and cooling the solution; melting the compound in the jelly state, hardened at a room temperature, into an organic solvent preferably methanol, to provide Yttrium-TFA/Barium-TFA/Copper-TFA solution for coating; depositing Yttrium-TFA/Barium-TFA/Copper-TFA solution for coating on a textured metal substrate having at least one oxide buffer layer atop or single crystal substrate with a thin thickness; after depositing the precursor solution, drying it to form a thin film; and applying a calcination and conversion heat treatments to the thin film to provide the thin film with a superconducting property.

Preferably, the operation of depositing a thin film may use a spin coating, a dipping coating, a spray coating, or a transfer system such as slot die coating.

Further, the operation of depositing a thin film is made atop of the textured metal substrate or single crystal substrate. Textured metal substrate and single crystal substrate may have a ceramic middle layer deposited thereon, functions to prevent the reaction with a superconducting layer on the metal surface and transfer the crystallinity of the biaxially aligned texture of substrate to the superconducting layer. Textured metal substrate is comprised of one among rolled heat-treated Ni, Ni-based alloy (Ni—W, Ni—Cr, Ni—Cr—W, etc.), silver or silver alloy, and cubic crystal metal such as Ni-silver complex or alloy. Single crystal is such as MgO(100), LaAlO₃(100), or SrTiO₃(100), etc.

Preferably, a total cation concentration of Yttrium-TFA/Barium-TFA/Copper-TFA solution for coating may be in the range of 0.1˜6 mol.

Preferably, the superconducting material powder may use REBa₂Cu₃O_(7-x) (RE=rare earth elements such as Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, etc. or mixture thereof).

Preferably, the organic solvent may be one selected from the group consisting of methyl alcohol, ethyl alcohol, methoxy ethanol (methylol glycol monomethyl ether).

Mode for Invention

Reference will now be made in detail to preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings.

In the following explanation, a description through accompanying drawings will be added in order to facilitate further complete understanding of the present invention, but it is apparent to those skilled in the art that the present invention can be carried out without a detailed description of the drawings.

In cases, a description of the main elements or constituents of the known technology will be omitted if it obscures the point of the present invention unnecessarily. This is intended to avoid anypossibility to obscure the description of the present invention.

FIG. 1 illustrates the method of producing a superconductor having a super conductivity, which is formed by preparing a precursor solution using an oxide powder and depositing it on a substrate, and then, performing a heat treatment thereon.

FIG. 2 illustrates a process of a calcination heat treatment of a superconducting material powder-TFA solution.

FIG. 3 illustrates a process of a conversion heat treatment of a superconducting thin film.

FIG. 4 illustrates an X-ray diffraction analysis result of the fabricated superconducting thin film.

Accordingly, it teaches that the oxide superconducting phase is aligned in a (c) axis.

FIGS. 5, 6, 7, 8 illustrate that superconducting crystal grains are formed from the result of examining micro structures of the specimen.

FIG. 9 illustrates the measurement result of a superconducting critical temperature of the specimen, which is converted into a superconducting state below 89.3 K.

FIG. 10 illustrates the measurement result of a superconducting critical current density of the specimen, in which a critical current density is 0.85 MA/cm<sup>2</sup> when a thickness of a thin film is 0.3 μm and a width thereof is 3 mm.

Now hereinafter, the method of the present invention will be explained taking an exemplary embodiment.

1/100 mol of a superconducting powder, YBa₂Cu₃O_(7-x) is solved into 30 cc of TFA acid aqueous solution. At this time, the solution may be heated in order to completely dissolve the superconducting oxide powder preferably below 80° C.

If the powder is completely dissolved and the solution is clear, the temperature of the solution is kept below 80° C. so as to vaporize the solution until the solution is changed into a viscous jelly state.

If the solution almost loses its fluidity, the heating is stopped and the solution would be cooled.

The compound in a jelly state, which is hardened at a room temperature, is dissolved into a 20 cc of methyl alcohol, to provide Yttrium-TFA/Barium-TFA/Copper-TFA solution for coating with 1-6 mol of a total cation concentration.

Dropping the precursor solution on a rotating substrate, a thin film is deposited on a LaAlO₃ single crystal substrate, or the deposition may use coating technique such as dipping, spraying, transferring, or the like, and then, through a drying process, a precursor thin film is formed.

A calcination heat treatment is carried out on the precursor thin film, as shown in FIG. 2, to vaporize solvent and impurities such as water and TFA acid and form a calcined thin film, and through a heat treatment as shown in FIG. 3, a superconducting phase is formed on the substrate.

The calcination heat treatment is carried out in the presence of oxygen, nitrogen, argon containing water vapor with a dew point of 20˜75° C., or mixing gas thereof, at a heating speed of 0.5˜1° C. per minute, and the heating is carried out up to a temperature of 300˜500° C., to decompose the metal organic precursor consisting of metal ions and TFA.

The conversion heat treatment is carried out by heating in the presence of nitrogen, or argon containing oxygen of 100˜1000 ppm and water vapor with a dew point of 20˜75° C., for 0.25˜4 hours at a temperature of 650˜850° C., so as to convert the calcined film into epitaxailly grown oxide superconductor thin film.

During conversion heat treatment, thin film is heated at a heating rate of 5˜20° C. per minute up to a temperature of 650˜850° C., and is maintained for 0.25˜4 hours until the calcined film, which consisted of oxides and oxyfluoride, is fully converted into REBCO oxide superconductor phase.</p>

In the temperature range of 400˜500° C. during the cooling, the thin film is maintained in a dry oxygen atmosphere for 1˜4 hours, so as to sufficiently fill the REBCO oxide phase with an oxygen gas so as to have superconductivity.

INDUSTRIAL APPLICABILITY

As described above, the present invention provides a method of fabricating a thin film superconducting conductor using REBa₂Cu₃O_(7-x) (RE=rare earth elements such as Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, etc. or mixture thereof), and in the method, a precursor solution is fabricated by dissolving REBa₂Cu₃O_(7-x) (RE=rare earth elements such as Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, etc. or mixture thereof) group of oxide into TFA acid aqueous solution, and using the precursor solution, a superconducting conductor can be provided. The precursor solution can be provided more easily with a lower price than a conventional precursor solution.

While the present invention has been described and illustrated herein with reference to the preferred embodiments thereof, it will be apparent to those skilled in the art that various modifications and variations can be made therein without departing from the spirit and scope of the invention. Thus, it is intended that the present invention covers the modifications and variations of this invention that come within the scope of the appended claims and their equivalents. 

1. A method of fabricating a precursor solution for metal organic deposition using a superconducting oxide as a starting material comprising a) dispersing a superconducting material powder in a TFA acid aqueous solution and heating them to dissolve the powder in the TFA acid aqueous solution; b) increasing a temperature of a hot substrate if the powder is completely dissolved, and the solution is clear, and continuously heating until the solution is vaporized and is in a viscous jelly state; c) stopping the heating if the solution loses its flowing property completely, and cooling the solution; and d) dissolving the compound in the jelly state, hardened at a room temperature, into an organic solvent, to provide a metal organic deposition solution for coating.
 2. The method as claimed in claim 1, wherein a total cation concentration of the organic deposition solution for coating is in the range of 0.1˜6 mol.
 3. The method as claimed in claim 1, wherein the superconducting material powder uses a powder of 123 compound prepared from a mixture of rare earth elements (Ya, Ybb, Smc, Lad, Nde, Hof, Gdg . . . )₁Ba₂Cu₃O_(7-x) (a+b+c+d+e+f+g+ . . . =1, 0<x<0.5).
 4. The method as claimed in claim 1, wherein the organic solvent is one selected from the group consisting of methyl alcohol, ethyl alcohol, methoxy ethanol (methylol glycol monomethyl ether).
 5. A method of fabricating a thin film-typed superconductor using a metal organic deposition method comprising: a) dispersing a superconducting material powder in a TFA acid aqueous solution and heating them to dissolve the powder in the TFA solution; b) increasing a temperature of a hot substrate if the powder is completely dissolved, and the solution is clear, and continuously heating until the solution is vaporized and is in a viscous jelly state; c) stopping the heating if the solution loses its flowing property completely, and cooling the solution; d) dissolving the compound in the jelly state, hardened at a room temperature, into an organic solvent, to provide a metal organic deposition solution for coating;</claim-text> e) depositing the metal organic deposition solution on a textured metal substrate or single crystal substrate with a thin thickness; f) after depositing the precursor solution, drying it to form a thin film; and g) applying a calcination heat treatment on the dried thin film to provide the thin film consisting of oxides and oxyfluoride. (h) applying a conversion heat treatment on the calcined thin film to convert into oxide superconductor phase of REBa₂Cu₃O_(7-x) (RE=rare earth elements such as Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, etc. or mixture thereof).
 6. The method as claimed in claim 5, wherein the step of depositing a thin film uses a spin coating, a dipping coating, a spray coating, or a transfer system such as slot die coating.
 7. The method as claimed in claim 5, wherein the operation of depositing a thin film is made atop of the textured metal substrate or single crystal substrate, and the textured metal substrate or single crystal substrate has a ceramic middle layer deposited thereon, and functions to prevent the reaction with a superconducting layer on the metal surface and transfer the crystallinity of the biaxially aligned texture of substrate to the superconducting layer, and the textured metal substrate is comprised of one among rolled heat-treated Ni, Ni-based alloy (Ni—W, Ni—Cr, Ni—Cr—W, etc.), silver or silver alloy, and cubic crystal metal such as Ni-silver complex or alloy, and the single crystal is such as MgO(100), LaAlO₃(100), or SrTiO₃(100), etc.
 8. The method as claimed in claim 5, wherein a total cation concentration of metal organic solution for coating is in the range of 0.1˜6 mol.
 9. The method as claimed in claim 5, wherein the superconducting material powder uses REBa₂Cu₃O_(7-x) (RE=rare earth elements such as Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, etc. or mixture thereof).
 10. The method as claimed in claim 5, wherein the superconducting material powder uses a powder of 123 compound prepared from a mixture of rare earth elements (Ya, Ybb, Smc, Lad, Nde, Hof, Gdg . . . )₁Ba₂Cu₃O_(7-x) (a+b+c+d+e+f+g+ . . . =1, 0<x<0.5).
 11. The method as claimed in claim 5, wherein the organic solvent is one selected from the group consisting of methyl alcohol, ethyl alcohol, methoxy ethanol (methylol glycol monomethyl ether).
 12. The method as claimed in claim 5, wherein a thickness of the final superconducting thin film is equal to or higher than 0.1 μm. 